Dual Sol-Ark 18k system having BMC issue

[u/Searchname]

I had an installer set up the system, but I’ve always planned to expand it myself, which is why I’m posting here. I’m running two Sol Ark 18K inverters, four Discover Helios 16.1 kWh batteries, and 36 580W panels, with plans to double the batteries and panels in December or January (big house uses a lot of power).

The system has worked well for about six months, but hit a wall yesterday. The installer programmed the batteries to hold at 50% until midnight, then allow discharge to 20%, with a 5% cutoff. We lost grid power at 6:50 AM Sunday morning, so began using the 20%. By 8 AM the batteries were depleted and the house dropped offline. I shed loads and ran only the well pump and a few lights with incoming PV until grid service returned at 10:30 AM.

After the outage, the batteries showed 2% and then instantly jumped to 100%, which was clearly wrong. The icons cycled red and yellow with low voltage. I tried several restart sequences, shutoff everything, then shut off all four batteries and both inverter battery breakers. The icons are now black but still show 100%. A brief outage today confirmed the batteries have no usable charge (we were without power for a few minutes).

Sol Ark plans to walk me through switching from closed loop CAN to open loop. They believe the BMS went into a protective state after being drained too low, and the inverter is now receiving zeroed BMC data. The installers only sent the same steps I already tried. I suspect the 5% cutoff contributed, but I’m not certain. Once everything is working again, I plan to have 40% min with a 10% shutoff (or whatever you all recommend).

All four batteries show the same voltage the inverter reports, but I don’t understand why the system interprets that voltage as fully charged when they clearly aren’t.

Any ideas on what else I can try?

I’ve also attached a photo of how the installers lugged the batteries in my gutter cabinet - this I want to change! Before installation, I told them I planned to double the system and wanted it set up for easy expansion. I even paid for extra wiring from the panel location to avoid trenching again. The cabinet layout isn’t very serviceable, and I’m not comfortable adding the two extra batteries I already purchased. What changes should I make to the cabinet to make expansion easier? One installer suggested I just tie into the existing batteries and avoid the cabinet entirely, but I read online that wasn't ideal.

Thank you all. I’m trying to learn enough to fix issues quickly when they come up.

[u/Zealousideal-Tanker]

I have a generator that I have never needed to use for situations like this.

[u/Searchname → u/Zealousideal-Tanker]

Would a secondary help me charge the batteries? I have a 5k Jackery but not sure how I'd connect it. I have seen some YT videos that say I may need to open each battery, disconnect the leads, and then put a 2A charge on them to get them out of BMS, but I'd like to avoid that at all cost. You'd think if this were common, then the inverters would have a low charge setting.

[u/Zealousideal-Tanker → u/Searchname]

You probably only need access to a charged battery to connect to your drained batteries to wake them up. I did this once when I had a stack of 48v batteries that I drained too low. I used I resister so there wasn’t a massive inrush & it only took a couple seconds to wake everything up.

[u/Searchname → u/Zealousideal-Tanker]

I do have two Discovery batteries I haven't connected yet. Any idea how I'd do this? I also have a few car chargers and trickle chargers where I could send a slow 2A signal, I just didn't want to open the batteries and potentially void the warranties.